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Posted by: Halfnelson Jun 20 2024, 03:33 AM

Had a previous thread starting in 2022 about my 73 1.7 standard D-Jet running way too rich and flooding to the point where it wouldn't start. It's been an ongoing issue. I've had a go. 2 garages have had a go. I'm at the point where I'm beginning to lose hope.

A recap. Bought the car 2021, had a problem with intermittent flooding. So far have:
Checked MPS - holding vacuum.
Replaced CHT sensor and tested. Working when flooded.
Replaced fuel pump and tested pressure.
Replaced all vacuum hoses and tested for leaks.
Valves set and rechecked.
New 123 distributor.
New injectors.

Each time I think I've cracked it and it runs and drives - sometimes for a month or so. Then I'll go to start it and it'll flood again to the point where it contaminates the oil. I feel like I've never managed to get to the bottom of the problem. Just keep replacing parts. Thinking maybe a return line that intermittently blocks? I'm kind of at a loss.

Posted by: emerygt350 Jun 20 2024, 04:20 AM

Have you removed the cold start valve from the equation?

Does it run rich or is the flooding happening when the car is off?

Posted by: Halfnelson Jun 20 2024, 04:51 AM

Yes, cold start valve has been bypassed. Car runs ok, put it away. Go to start it from cold a few days later and it just doesn't fire up. If I keep trying then it just floods the engine with petrol to the point it comes out of the exhaust.

Posted by: JeffBowlsby Jun 20 2024, 06:01 AM

The MPS holding vacuum is not a definitive test. I've seen several MPS that hold vacuum and yet the diaphragm is fractured, sometime completely. I would open that MPS up to verify the diaphragm condition and replace the diaphragm if its torn.

Posted by: Halfnelson Jun 20 2024, 06:31 AM

Thanks Jeff, Is there a way to check without breaking the unit open? If I do I guess it would then need recalibrating?

Posted by: Halfnelson Jun 20 2024, 06:33 AM

Also would that present as an intermittent issue as it has had a few runs where it's seemed to be fine?

Posted by: emerygt350 Jun 20 2024, 06:40 AM

It could. Just depends on how it is cracked. I know guys have borrowed mps before. Maybe somebody could lend you the right model and you could do a quick swap to see if that is actually the problem.

Posted by: JeffBowlsby Jun 20 2024, 07:10 AM

A visual diaphragm check requires opening it for inspection.

If you are very careful, and use a micrometer to set the inner screws to a new diaphragm (the Chris Foley method) you may not need to calibrate it. Potentially be prepared to open it more than once to fine tune. This method an avoid needing to remove the epoxy plug and WOT stop. Its delicate work, but possible.

Posted by: JeffBowlsby Jun 20 2024, 07:11 AM

Thats exactly how it would behave.

Posted by: Halfnelson Jun 20 2024, 07:19 AM

Thanks Jeff, I’ll have a read up on the process to see if it’s in my skill set.

Posted by: emerygt350 Jun 20 2024, 08:35 AM

If you get the rebuild kit from Chris it is super easy and inexpensive. The more difficult part is tuning it. I agree with Jeff, if you are super careful about recording where the inner, outer, and full stop is when you disassemble, you 'should' be able to put it back. If you get a cheap lcr and vacuum pump you could measure the inductance and make sure they are the same when you reassemble. No guarantees of course. The physical repair is super easy.

Posted by: emerygt350 Jun 20 2024, 08:37 AM

I wonder about the ECU... They rarely go but perhaps this is one of those moments? Do you know the number on it?

Posted by: rjames Jun 20 2024, 09:10 AM

I agree with emerygt350 in suggesting the ECU. In fact I had to replace mine because it was doing the exact same thing as yours. It would drive fine for hours and then out of the blue go full rich and stall. I chased my tail for months because I bought into the 'ECUs rarely fail' myth. I had to go through 3 ECUs (including a truly NOS ECU) before finding one that worked properly.

Try and find a known good ECU to test before opening up the MPS.

Posted by: rjames Jun 20 2024, 09:10 AM

double post

Posted by: emerygt350 Jun 20 2024, 09:15 AM

I have a known working extra 037 from my 73 2.0. I believe they are the same units the 1.7 used that year.

Posted by: StarBear Jun 20 2024, 09:16 AM

@http://www.914world.com/bbs2/index.php?showuser=24231 @http://www.914world.com/bbs2/index.php?showuser=8571 B @http://www.914world.com/bbs2/index.php?showuser=15080
Hence, our L-Jets. Trade-off: our vacuum senisitivity for D-Jet MPS sensitivity.

Posted by: FlacaProductions Jun 20 2024, 09:34 AM

What MPS do you currently have? I believe a 73 1.7 should be an 049.

From my notes, @http://www.914world.com/bbs2/index.php?showuser=25740 - the 037 is for an early 73 2.0.

Posted by: 914_teener Jun 20 2024, 11:02 AM

There you go. First task, make sure your parts are correct for the displacement.

Posted by: Ishley Jun 20 2024, 11:55 AM

It sounds a lot like you're having ignition and spark issues. I chased a lot of issues before I realized I had a spark plug wire issue that would intermittently cause misses.... and my car would run very rich. Chasing down problems and checking plugs etc.... I would move the suspect wire... and then it would run fine... for a while. Sometimes if you're lucky... it's the simple things.

Another issue I had earlier... was the seating of the 123 Distributor. The my unit came with a spacer ring... which I added... and I found that to be a problem. Once I removed it... it seats better and is really locked in place.

Also... with the 123 Distributor.... make sure the two wires that are connected to 914 harness are making solid connections.

What are your plugs gapped to? Too small/big and you can have misfire issues... The 123 with the right coil should give you a healthy fat spark. Do you replace your plugs after a rich running cycle? They could be fouling over and over... and slight misfires will appear as rich.

Is your coil good? Do you have the correct one for the 123 distributor?

Another issue could be the Throttle position sensor. It underneath the throttle valve. There is an adjustment procedure that needs to be right. If the adjustment screws are not holding it firmly in place.... you can get weird issues. This can be replaced too.... at the very least make sure your injector harness is solidly connected to the TPS.

Do you have a fuel pressure gauge installed in the engine bay? I would recommend it and make sure you have a consistent rate of fuel. Easy install and worth knowing where your pressure is at.

The MPS rebuild could be your issue... I did mine... but in my opinion....you're are moving into a complex area with this... and the tuning afterwards can be complicated and is really best done with a Wideband O2 sensor installed in your exhaust and an Air Fuel Ratio Gauge that is wired to a dash gauge for monitoring. I would make sure everything else is working right first before I jumped into this.

Check and recheck all the easy stuff with your Ignition system. Your clearly getting fuel.

Posted by: FlacaProductions Jun 20 2024, 12:47 PM

Agreed on MPS tuning - that's a whole different game. I was thinking that maybe a quick swap to another unit might help rule it in/out.

Posted by: emerygt350 Jun 20 2024, 03:06 PM

I believe there were no differences between the early 2.0 ECU and the 1.7. they just cheated with a spacer in the MPS and a richer head temp sensor. They cheaped out as best they could that first year of the 2.0.

Posted by: JamesM Jun 20 2024, 04:18 PM

ECU is the same in 73 for 1.7s and 2.0s but everything else is different. MPS differences are more than just a spacer ring.

As stated:
#1 make sure all your parts are correct, should have yellow (or possibly black) injectors. 037 ECU, 049 MPS (041,042 could get you by though)(NOT 043, or 037)

#2 make sure all your parts are adjusted and tested to spec

I find the majority of rich mixture issues are due to the MPS, followed by the head temp sensor. Most other faults cause a lean condition. If you are running the 037 MPS that has a good chance of explaining why you are rich. If you are running the proper MPS but it has been previously opened that might also explain the issue as you have no idea what has been done to the diaphragm or how it has been adjusted.

There really isnt that much involved to diagnose this issue, only roadblock is verifying proper MPS operations as you pretty much need a known good one on hand even if you have an inductance meter to test one electronically. If everything else is passing basic bench tests, chances are its most likely the MPS.

Posted by: emerygt350 Jun 20 2024, 04:26 PM

My point was, he could borrow my ECU.

Posted by: JamesM Jun 20 2024, 09:45 PM

If you want to rule it out they should be the same. I generally try and disrupt that connection as little as possible and in my experience ECU is usually the last thing to fail and the few i have seen with issues fail either not firing one of the injector banks or not powering the fuel pump. Intermittent over rich flood condition, my bets are MPS or CHT.

if the CHT wire losses continuity/gains infinite resistance the systems goes puke rich to the point of stalling.

If the MPS looses vacuum intermittently it goes WOT rich. I have seen this happen with diaphragm cracks that dont always show up with bench vacuum tests.

Posted by: 914_teener Jun 20 2024, 10:01 PM

I'm with Jeff. This is a common failure mode of the MPS.

If I were you I'd have it look at. If you feel you don't have the skills just send it to Jeff.


I had this exact problem.....would hold vacuum to an extent but was as it turned out a cracked diaphragm.

BTDT.

Posted by: rjames Jun 20 2024, 11:09 PM

The ECU is the easiest thing to test first. Move to the MPS afterwards.

Posted by: emerygt350 Jun 21 2024, 05:14 AM

The intermittent cht is an interesting idea but it seems like something that would go while driving. Jiggle test?

The sitting and losing it makes me think more on the lines of broken logic control in the ECU. Some combination of signals resulting in pig rich when it shouldn't. Mps of course is the major suspect. If you do want to try my extra ECU, just let me know. One more thing you could exclude before tackling the MPS.

Posted by: ClayPerrine Jun 21 2024, 05:28 AM

For years the rule of thumb was "The ECU never breaks. It is the last thing you suspect or change." But 50 + years have passed, and they are starting to break from vibration and old age.

This sounds like an intermittent ECU issue to me.

Posted by: JeffBowlsby Jun 21 2024, 05:32 AM

While the idea of swapping in 'known good' parts like the ECU is noble, I have seen some 'known good' ECUs be functionally defective in some mode even though they seem to work OK. No harm in trying the swap as a first step as it may get one closer to any issue and solution. But that process is not definitive.

I have the equipment to test the ECUs, D-Jet or LJet, but I don't do repairs. Or send it to an ECU repair shop for their analysis and any needed repair. Verify functionality of every ECU function and take the guess work out of the equation.

Posted by: emerygt350 Jun 21 2024, 06:31 AM

If cost is no issue, definitely send it out for testing. I would start with jiggling that cht wire while the car is running, that should run 0 dollars and 2 minutes time. Double check the MPS, you may catch it in a failed state. You could check the resistance as well. If neither of those turn up anything and you want to try my ECU, let me know. If that does nothing, I would say Chris's kit might be smart. If nothing else, your mps will be ready for another 50 years and tunable without disassembly.

Posted by: emerygt350 Jun 21 2024, 06:33 AM

Just a quick mention on the TPS, although I really don't think it could cause this, even in a failed state, but the car will run perfectly fine with it unplugged, so you may want to just try unplugging it and see what happens.

Posted by: ClayPerrine Jun 21 2024, 07:19 AM

But the downside to bench testing and ECU is that is is not subjected to engine heat and vibration when you do this. So intermittent connection issues won't show up.

If there is a break in the CHT circuit, the ECU is designed to go full rich. So a solder joint inside the ECU in the CHT circuit, broken due to vibration or heat, could cause a intermittent flooding condition.

Another could be an old wire in the CHT circuit the harness that is old and brittle. Vibration causes it to move enough to break the circuit, and it goes full rich.

Or the connector between the CHT and the harness is corroded or making a bad connection.

The last two can be resolved with a new harness. The ones Jeff makes are excellent and resolve a LOT of running issues with D-Jet, or even L-Jet. So if you have not bought one of the new harnesses, I would suggest it.

Jeff. You can send my sales commission to me via paypal.

Posted by: dr914@autoatlanta.com Jun 21 2024, 08:22 AM

substitution is your friend. That is what we do here to save time and frustration. MANY also send us their components for testing on another 914

Posted by: Halfnelson Jun 22 2024, 04:27 AM

Thanks so much for the suggestions. I’ve been through the list of part numbers and can confirm they are correct for a 73 1.7 so no parts have been mismatched previously. The MPS hasn’t previously been opened and I had hoped the 123 would mate sure the spark was good and consistent but I’ll double check this and leads (which should also have been new).

Thanks so much for the kind offer of a loan of an ecu and if I was stateside I would gladly take you up on it, but I’m in the UK. I’ll try and source ecu and mps to swap and see.

If it does come to rebuilding mps is there a specialist who can do this?

Posted by: Halfnelson Jun 22 2024, 04:32 AM

I’m not sure if this is relevant but when it does flood, if I unplug the injectors, turn the engine over, after a few cranks it’ll fire up and run for a few seconds on the fuel already in the system, then die. If I plug in the injectors then it’ll fire up and run. However it’s flooded so badly that the oil now smells of fuel.

Posted by: ClayPerrine Jun 22 2024, 04:39 AM

That really sounds like the CHT is open circuiting. I would find a good CHT (not the junk aftermarket ones currently available) and replace it. It is approximately $25.00 US, so it is a cheap investment to try to fix it.

And change the oil soon.

Good luck!

Posted by: emerygt350 Jun 22 2024, 04:53 AM

Ahh, Cornwall, just noticed that.

Can you describe exactly when this is happening?
1) Do the cylinders fill while it is sitting or is this only once you try to restart the car?

2) does it run rich when it is running but not flooded?

Posted by: Halfnelson Jun 22 2024, 05:13 AM

Although the cht has been changed and I’ve tested it a couple of times, once when running ok, once when it wouldn’t start, I have an another new one to swap in. I’m also going to test it from ecu plug 23 to see if it’s something in the wire.

Re rich running, I think the car is running too rich generally. I swapped out the plugs and they were black and sooty. I guess it could be flooding when I turn the engine off? Hadn’t thought of that. It sometimes stands for a week or two and then I go to start it and it doesn’t even try to fire, it just cranks with no attempt to fire up, not even a splutter.

When it does fire it fires first crank… like the moment I turn the key from the pump priming to the starter.

Posted by: ClayPerrine Jun 22 2024, 06:27 AM

Where and when did you get the CHT? The current batch of aftermarket ones are having issues....

http://www.914world.com/bbs2/index.php?showtopic=360631

Hope that helps.

Posted by: technicalninja Jun 22 2024, 03:47 PM

What he's describing appears to be fuel fouling BEFORE he tries to start it.
Sounds like it doesn't even bark or cough for him.
He's WET!

And it's intermittent...


Next time it doesn't start I'd pull a plug IMMEDIATELY and check for wet.
If the plug was dry enough to fire I'd verify spark next.

Does it run a vacuum referenced FP regulator?
If so, check the vacuum line for evidence of fuel
That's almost NEVER intermittent, but it doesn't take long to verify.

I'm interested in what it turns out to be.

Posted by: technicalninja Jun 22 2024, 03:59 PM

Made me think...

An ECU that did short the injectors to ground, intermittently, might be able to create what is occurring.

It's another easy test for me.

Get a Noid light/injector pulse tester.

https://www.amazon.com/PANNUOSCS-Light-Injector-Tester-%EF%BC%8811-Piece%EF%BC%89/dp/B0BNPFLHLJ/ref=asc_df_B0BNPFLHLJ/?tag=hyprod-20&linkCode=df0&hvadid=693401379483&hvpos=&hvnetw=g&hvrand=17017925232780847571&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1026438&hvtargid=pla-1946304855017&psc=1&mcid=2f36b0d1f41637d991000fbcc40e5205&gad_source=1

Plug the appropriate size into injector harness.
Burn when ignition on/engine off?

Bad ECU or intermittent short to ground in wiring harness (it IS 50 years old!)

Note: I'm novice at D-Jet but Master at L-Jet and modern.
Sometimes I give poor advice on D-Jet stuff. Take my advice with a grain of salt.
I am trying to help.

Posted by: emerygt350 Jun 22 2024, 04:03 PM

Pressure Regulator on these is static. The wet plug would be a good and easy check.

Posted by: Halfnelson Jun 23 2024, 05:08 AM

Do you recommend pulling a plug, checking, and then trying to fire it up. Surely if I test after it fails to start it’ll be wet from the unburnt fuel.

Posted by: emerygt350 Jun 23 2024, 06:01 AM

Yeah, check first and then after if it doesn't start. Hell, check even if it does start.